The present invention relates to a semiconductor device, a semiconductor module and a hard disk, and especially to a structure capable of efficiently dissipating heat from a semiconductor chip.
Due to the recent growth of the use of semiconductor devices in portable devices and small/densely-mounted devices, the reduction in size and weight and the improvement in heat dissipation properties are demanded at the same time. In addition, semiconductor devices are mounted on various types of substrates, which, in turn, are mounted in various many systems as semiconductor modules. As for such a substrate, the use of a ceramic substrate, a printed board, a flexible sheet, a metal substrate or a glass substrate etc. may be contemplated, and the following description gives one example thereof. Here, the semiconductor module is explained as being mounted on a flexible sheet.
FIG. 14 shows an example in which a semiconductor module using a flexible sheet is mounted in a hard disk 100. This hard disk may be, for example, the one described in detail in an article of Nikkei Electronics (No. 691, Jun. 16, 1997, p. 92-).
This hard disk is accommodated within a casing made of a metal, and comprises a plurality of recording disks that are integrally attached to a spindle motor. Over the surfaces of individual recording disks, magnetic heads are respectively disposed each with a very small clearance. These magnetic heads are attached at the tips of suspensions which are affixed to the ends of respective arms. A magnetic head, a suspension and an arm together form one integral body and this integral body is attached to an actuator.
The magnetic heads must be electrically connected with a read/write amplifying IC in order to perform read and write operations. Accordingly, a semiconductor module comprising this read/write amplifying IC mounted on a flexible sheet is used, and the wirings provided on this flexible sheet are electrically connected, ultimately, to the magnetic heads. This semiconductor module is called “flexible circuit assembly”, typically abbreviated as “FCA.”
From the back surface of the casing, connectors provided on the semiconductor module are exposed, and these connector (male or female) and connectors (female or male) attached on a main board are engaged. On this main board, wirings are provided, and driving ICs for the spindle motor, a buffer memory and other ICs for a driving, such as ASIC, are mounted.
The recording disk spins at, for example, 4500 rpm via the spindle motor, and the actuator detects the position of the magnetic head. Since this spinning mechanism is enclosed by a cover provided over the casing, there is no way to completely prevent the accumulation of heat, resulting in the temperature rise in the read/write amplifying IC. Therefore, the read/write amplifying IC is attached to the actuator or the casing etc. at a location having a better heat dissipation property than elsewhere. Further, since revolutions of the spindle motor tend to high-speed such as 5400, 7200 and 10000 rpm, this heat dissipation has more importance.
In order to provide further detail of the FCA explained above, the structure thereof is shown in FIGS. 15A and 15B. FIG. 15A is the plan view, and FIG. 15B is a cross-sectional view taken along the line A—A which cuts across a read/write amplifying IC 115 provided on one end of the module. This FCA 117 is attached to an internal portion of the casing in a folded-state, so that it employs a first flexible sheet 116 have a two-dimensional shape that can easily be folded.
On the left end of this FCA 117, the connectors 111 are attached, forming a first connection section 120. First wirings 121 electrically connected to these connectors 111 are adhered on the first flexible sheet 116, and they extend all the way to the right end. The first wirings 121 are then electrically connected to the read/write amplifying IC 115. Leads 122 of the read/write amplifying IC 115 to be connected to the magnetic heads are connected with second wirings 123 which, in turn, are electrically connected to third wirings 126 on a second flexible sheet 124 provided over the arm and suspension. That is, the right end of the first flexible sheet 116 forms a second connection section 127 at which the first flexible sheet 116 is connected to the second flexible sheet 124. Alternatively, the first flexible sheet 116 and the second flexible sheet 124 may be integrally formed. In this case, the second wirings 123 and the third wirings 126 are provided integrally.
On the back surface of the first flexible sheet 116 on which the read/write amplifying IC 115 is to be provided, a supporting member 128 is disposed. As for this supporting member 128, a ceramic substrate or an Al substrate may be used. The read/write amplifying IC 115 is thermally coupled with a metal that is exposed to inside of the casing through this supporting member 128, so that the heat generated in the read/write amplifying IC 115 can be externally released.
With reference to FIG. 15B, a connecting structure between the read/write amplifying IC 115 and the first flexible sheet 116 will now be explained.
This flexible sheet 115 is constituted by laminating, from the bottom, a first polyimide sheet 130 (first PI sheet), a first adhesion layer 131, a conductive pattern 132, a second adhesion layer 133 and a second polyimide sheet 134 (second PI sheet), so that the conductive pattern 132 is sandwiched between the first and second PI sheets 130 and 134.
In order to connect the read/write amplifying IC 115, a portion of the second PI sheet 134 and the second adhesion layer 133 are eliminated at a desired location to form an opening 135 which exposes the conductive pattern 132. The read/write amplifying IC 115 is electrically connected thereto through leads 122 as shown in the figure.
The semiconductor device packaged by an insulating resin 136 as shown in FIG. 15B has heat dissipating paths indicated by arrows for externally dissipating its heat, but there has been a problem in that, due to the thermal resistance given by the insulating resin 136, the heat generated by the read/write amplifying IC 115 cannot be efficiently dissipated to the outside the device.
Further details will now be explained using this example in hard disk application. As for the read/write transfer rate of a hard disk, a frequency of 500 MHz to 1 GHz, or even a greater frequency, is required, so that the read/write speed of the read/write amplifying IC 115 must be fast. To this end, the paths of the wirings on the flexible sheet that are connected to the read/write amplifying IC 115 has to be reduced, and the temperature rise in the read/write amplifying IC 115 must be suppressed.
Especially, since the recording disks are spinning at a high speed, and the casing and the lid provide a sealed space, the interior temperature would rise up to around 70 to 80° C. On the other hand, a typical allowable temperature for the operation of an IC is approximately 125° C. This means that, from the interior temperature of 80° C., a further temperature rise by approximately 45° C. is permissible for the read/write amplifying IC 115. However, where the thermal resistance of the semiconductor device itself and FCA is large, this allowable operation temperature can easily be exceeded, thereby disabling the device to provide its actual performance level. Accordingly, a semiconductor device and FCA having superior heat dissipating properties are being demanded.
Furthermore, since the operation frequency is expected to further increase in the future, further temperature rise is also expected in the read/write amplifying IC 115 itself due to the heat generated by computing operations. At room temperature, the IC can provide the performance at its intended operation frequency, however, where it is placed inside of a hard disk, its operation frequency has to be reduced in order to restrain the temperature rise.
As described above, further heat dissipating properties of semiconductor device, semiconductor module (FCA) are demanded in connection with the increase of the operation frequency in the future.
On the other hand, the actuator, and the arms, suspensions and magnetic heads attached thereto has to be designed as light-weighted as possible in order to reduce the moment of inertia. Especially, where the read/write amplifying IC 115 is mounted on the surface of the actuator, the weight reduction is demanded also for the IC 115 and FCA 117.